Ok, this came up last year on my trip to WY, and I had a suspicion. Now, I think I may have figured out a big piece of this little puzzle.

Last year, my hard wired RV CO detector started going off in the middle of the night, for no apparent reason. I suspected maybe a leak in the Aquahot exhaust. The bus engine wasn't running, and hadn't been for several hours.

So earlier this week, with the bus parked in the driveway, I turned on the basement A/C to cool it down inside so I could rewire my fridge's defroster circuit (another puzzle for another thread). I left it running for a time, and came back out to hear the CO detector going off. I disconnected it.

Last night, my daughter wanted to have a sleepover in the bus, so I turned on the A/C for them, and plugged in a Nighthawk household CO detector I have. I came out about 2 hours later, and it was registering 122 on the readout. Turned off the A/C and opened the power vents and the reading started to come down immediately. This morning, the reading was 0.

It's obvious now that the problem is occurring because of running the A/C. Now I know the A/C doesn't produce CO, and there's no combustion going on anywhere. The AquaHot is turned off. The bus hasn't been run for several days. The propane is turned off, so no stove. It has to be coming from the A/C.

That leave me to believe there may be a small freon leak in the Coleman Basement A/C, and the freon is being detected by the CO detector.

Has anyone else experienced this?

Nick, do you know anything about the freon used in these Coleman dual compressor systems (probably R22. Maybe R134)?

Do you have a propane 'fridge? Sometimes, if it's not sealed really well and if there's a leak in the supply duct work, outside air can be drawn in. If the air being drawn in is from around the 'fridge or its vent, you could have CO coming inside. It's just a thought, but I had a duct leaking in my crawlspace at home and it would cause air to be pulled in from leaks around windows, doors, range hood, etc when the HVAC was on.

My wife just called and said the CO detector was up to 98 and blasting it's warning. The A/C hasn't been turned on since last night, but the vent has been closed since about 3 am when it rained.

I found some stuff online which indicates the older CO detectors (of which this is one) can be cross-sensitive to other chemicals, and freon was one of those. It also said that humidity affects the sensitivity and higher humidity (like today) can result in more false alarms.

I really think there must be a freon leak in the A/C, though, that is being detected by the CO detector. The RV CO detector was plugged in for a several weeks, including a trip to WY a few weeks ago, and it didn't have any problems until I turned on the basement A/C the other night (didn't use the basement a/c on the trip to WY).

I know a couple guys who work with a/c. Maybe one of them has a freon sniffer.

Your basement air has a drain pan in it that is holding a certain amount of still water in it, that water has a mixture of dust, algie, andsome mold that produces small amounts of gasses. Theese gasses are then picked up by your blower and sent through the coach.They are not harmful unless you have large signs of mold!! Than a good bleaching would cure that.That is one of the reasons that home CO detectors don't work in small places.

The thought of something growing in the A/C evaporator area had actually crossed my mind, but I couldn't figure out how it would set off the detectors. Production of methane could certainly explain it, as I think that may have been one of the things the detectors can be overly sensitive to. My other thought was possible outgassing from the Polyiso insulation, but that's been in for some time, so shouldn't be giving off much of anything anymore.

So evidently, the RV detectors are no better at filtering that stuff out than the household models are because my RV unit was alerting on it too.

So, would squirting some clorox into the evaporator help, or would that just create chlorine in the air which would also set off the alarm.

It seems that while it was a great safety idea, CO detectors (even the RV model) are probably not suited for the bus.

Over the years I have seen some odd things with CO detector and eveb smoke detectors to some extent.

When Luan paneling was prevalent in RV's and van conversions some of the chemicals used in the manufactureof the paneling would leech out and into the air and actually trip detectors.

Paints, Stains, Varnishes, sealants spray foam and canned foam can all leech fumes into the air which couldbe detected by those electronic noses. Even cleaners like Chlorox Cleanup leave a residual smell and potentiallycan leech into the air in a confined space. Automotive fabrics also leak chemical vapors, that's that new car smell!

My trick to solving that mysterious CO detector "creep" was to run a small ventilation fan to keep the air changedon a continuous basis. I left my range hood fan on for 6 years. when I turned it off for 12 hours the invisibleCO "creeper" would start counting up. I found that something like 100 cuft/hour was enough to keep the detectorfrom counting and alarming.

Also if it is mounted on a wood surface might I suggest that you get a small sheet of plastic or mylar and insulatethe detector away from direct contact with painted/stained or laminated surfaces.